xxxii Inteoduction to the Makeestoun Obseevations, 1843. 



turned through 69° 44', reading A 287° 44', the scale reading being 148. The 

 westerly declination during adjustment was 25° 28'. 



November 8^ 21"" 20"". The bifilar magnet was removed in order to determine its 

 temperature correction ; the brass weight being substituted, the arms of the torsion 

 circle were turned from A 287° 44' to A 357° 30', when the collimator scale read 

 157*5, or 9'5 scale divisions greater than on April 28, the westerly declination being 

 25° 20'. As it is necessary to determine the changes of horizontal force during the 

 observations for the temperature correction, the magnet used for deflections in ob- 

 servations of absolute horizontal intensity was substituted. The moment of this 

 bar was found too great for grooved wheel No. 8, previously in use (Introduction, 

 1841-2. 30.), wheel No. 9 was substituted, whose diameter = 0*459 inch ; as the 

 diameter of wheel No. 8 = 0*409 inch, and the value of one division of the micro- 

 meter-headed screw = 0*0005194 inch, the wires were rendered parallel by turning 

 the micrometer head through 96 divisions. 



The brass weight being suspended, the scale reading was 128*5 

 The magnet 126*0 



The weight being suspended, the arms of the torsion circle were turned through 90°, 

 when it read, vernier A 178° 0', B 358° 0'; the collimator was then turned by its 

 independent motion till the scale reading was 143 ; the magnet was suspended, and 

 the scale reading was found 142 when the arms of the torsion circle were turned 

 through 55° 17'-5, the circle reading A 122° 41 '-5, B 302° 43'. 



November 10** 6^. The temperature experiments having been made, the de- 

 flecting bar in the bifilar magnetometer was removed, and the arms of the torsion 

 circle were turned from B 302° 43' to B 358° nearly, when the scale reading was 143, 

 as in the previous adjustment. Wheel No. 9 was removed, and No. 8 substituted, 

 the micrometer head being turned backwards through 96 divisions. 



y The bifilar magnet being suspended, the scale reading was 93 

 The brass weight 96 



the arms of the torsion circle were turned through 90°, when the reading was B 

 358° 35' ; the collimator was turned by its independent motion till the scale reading 

 was 172*4, the magnet was inserted and the arms of the torsion circle turned through 

 68° 18', when the torsion circle reading was B 290° 17', and the scale reading 173°. 

 The bifilar thermometer 42°*4, and the absolute westerly declination 25° 18'. 



39. The following are the values of v, of k =z a cot v, and of q' =-, with the 

 periods to which they apply in 1843. 



